Microelectromechanical systems (“MEMS”) designers face a number of design considerations. For example, reducing the footprint of a chip is an ever-present goal in microelectromechanical systems (“MEMS”) design. One problem that is often encountered is the need for a MEMS and an integrated circuit such as an application specific integrated circuit (“ASIC”) chip to act together. In some instances, performance is improved if the MEMS and the ASIC are located near to one another. Accordingly, it is desirable to package these components near one another.
Another goal of MEMS design is reducing the influence of undesired stress on the MEMS. A major source of package stress on MEMS devices is a mismatch of the coefficient of thermal expansion (“CTE”) between device materials. This is commonly seen in the CTE mismatch between an organic substrate material such as FR-4 and a silicon device. FR-4 has a CTE of ˜14 ppm/° C. while silicon has a CTE of 2.9 ppm/° C. Such a CTE mismatch induces stress when the temperature changes if these two materials are adhered to each other using a stiff solder.
A critical feature of many MEMS devices is a hermetic seal that prevents the flow of water into the device. If water or water vapor seeps into a MEMS package, capacitances that affect performance of the MEMS can vary uncontrollably, negatively impacting function. Accordingly, it is desirably to seal MEMS from the environment.